Rage
~~~~~
Guardian: 1/1
Grim Inspiration: 3/3 - Every weapon you own will be modded. This maxes Rage meter quickly.
Guardian Spirit: 1/1
Righteous Fire: 3/3 - Most kills will be with guns later on. This maxes Rage meter quickly.
Guardian Angel: 1/1

Combat
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Sharp Weapons: 1/1
Hard Knocks: 3/3 - Your Boost Aura raises this skills damage by an additional 25% (Melee)
Gender Wars: 3/3 - Your Boost Aura raises this skills damage by an additional 25% (Male enemies)
Firearms Training: 1/1
Cold Rage: 3/3 - Allows for critical hit mayhem after every kill.
Wunderwaffe: 3/3 - Your Boost Aura raises this skills damage by an additional 25% (Modded Guns)
Gun Kata: 1/1

Survival
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Boost Mood: 1/1
Pick Lock: 3/3 - I've yet to find a good weapon in a locked box. But a better choice then the other two options.
Custom Maintenance: 3/3 - Your Boost Aura raises this skills durability by an additional 30% (Modded Weapons)
Boost Ambiance: 1/1
Recycler: 3/3 - Craft your own ammo instead of trying to find Human enemies to kill.
Rain of Bullets: 3/3 - Carry a boat load of ammunition at once.
Boost Aura: 1/1

I'd go down the Survival Tree first until I get to Boost Ambiance. There's no point taking Recycler and Rain of Bullets right away because you won't have any Guns to use yet. Then I'd go down the Fury tree until get to Righteous Fire. At this point you start finding guns and can finish Fury and Survival at the same time. Then go for the Combat tree. With this build you have 10 points left over. I'd then pick:

Volatile: 3/3 - Fills your Rage meter faster.
_____________: 3/3
Attack Formation: 3/3 - More damage for your entire team during Fury
Maintenance: 1/3 - Your Boost Aura raises this skills durability by an additional 25% (Melee Weapons)

The blank space I have no idea what I'll pick. Maybe Jackpot (+15% more Rare Loot) or Executioner (Critical Chance +3%) or Recovery (60% chance not to get staggered)